This project alms to expand the understanding of how to slow the accumulation of weight in childbearing women by developing, implementing and evaluating two electronically-mediated (web-based) behavioral interventions, one for pregnant women and one for postpartum women. The goals of the interventions are, respectively, to decrease the prevalence of excessive weight gain during pregnancy and excessive weight retention (>5 pounds) in the first 18 months postpartum in a racially/ethnically diverse sample of both higher and lower income (<185% of the poverty line) women who enter pregnancy with normal (19.8-26.0), overweight (26.1-29.0), and obese (>29.0) body mass indices (BMI). In phase 1, the electronically-mediated behavioral interventions (e-interventions) will be either adapted or newly developed, and then tested. In phase 2, a randomized controlled trial will be conducted to evaluate the efficacy of the pregnancy e- intervention alone and in combination with the postpartum e-intervention. Five thousand women in the first 20 weeks of pregnancy will be randomized to one of three groups: Intervention Group 1 will receive the electronically-mediated behavioral intervention program only during pregnancy (e-interventlon 1). Intervention Group 2 will receive e-intervention 1 plus an electronically-mediated intervention for 18 months postpartum (e-intervention 2). Control women will receive non-weight related content at the project web site. The primary hypotheses are as follows: H1: The proportion of women in Intervention Groups 1 and 2 (combined) who gain more weight in pregnancy than is recommended by the Institute of Medicine will be 33% less than the proportion in the Control Group who gain excessively. H2: The proportion of women in Intervention Group 1 and Group 2 who retain more than 5 pounds at 6, 12, and 18 months postpartum will be reduced by 33 to 50% compared to the Control Group (each Intervention Group compared to Control Group). H3: The Control Group will have a higher mean weight retention and a smaller proportion of women returning to their pre-pregnancy weights at 6, 12 and 18 months postpartum than Intervention Group 1, and Intervention Group 1 will have a higher mean weight retention and a smaller proportion of women returning to their pre-pregnancy weights than Intervention Group 2 at the three postpartum time points. Research questions concerning genetic susceptibility to weight gain and behavioral mediators of intervention effects will also be addressed. RELEVANCE (See instructions): This project aims to discover strategies that will help women avoid excessive weight gain, a risk factor for cardiovascular disease, during the childbearing years. The project uses the Internet to efficiently reach a large group of pregnant women who are likely to be receptive to health information. The project has the potential to decrease the proportion of young women who become obese by mid-life. (End of Abstract)